US6221012B1 - Transportable modular patient monitor with data acquisition modules - Google Patents

Abstract

Patient monitoring apparatus for use in an environment which includes a plurality of sensors. The apparatus provides collection and display of patient data signals collected from a medical patient using the sensors, including periods when the patient is being transported. The apparatus comprises a portable monitor coupled to a plurality of distinct data acquisition modules, which are coupled to the sensors. The modules includes cartridges, which detachably mount to the portable monitor, and pods which are positioned independent of the monitor. The pods reduce the number of cables extending between the patient's bed and the portable monitor by combining signals from many sensors into a single output signal. The modules collect patient data in analog form from the sensors and provide digital data signals to the monitor. The portable monitor includes: a display device for displaying the patient data, and storage for the patient data. The portable monitor may be coupled to a docking station. The portable monitor receives power from the docking station, and transfers data to a remote display device by way of the docking station. Patient data is displayed on either one of the portable monitor or the remote display device. A battery pack and a hardcopy output device attach to the case of the portable monitor.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of Ser. No. 07/989,415 filed Dec. 11, 1992 now abandoned.

FIELD OF THE INVENTION

The present invention relates to medical systems and in particular to patient monitoring systems for collecting, storing and displaying medical data.

BACKGROUND OF THE INVENTION

In hospitals and other health care environments, it is often necessary to continually collect and analyze a variety of medical data from a patient. These data may include electrocardiogram signals, body temperature, blood pressure, respiration, pulse and other parameters.

Monitoring systems in the related art have typically fallen into one of two general categories: multi-function monitoring, recording and displaying systems which process and collect all of the data desired, but are bulky and difficult to transport; and small, portable systems which are easy to transport, but process and collect fewer types of data and have limited storage capability. Initially (e.g., in an ambulance or an emergency room) a patient is connected to a simple, portable monitor to observe a limited number of medical attributes, such as EKG or non-invasive blood pressure. As the patient moves to higher care facilities (e.g., an intensive care unit or operating room) it is desirable to augment these simple monitors to observe additional parameters. Generally, this is accomplished by disconnecting the patient from the simple monitor and connecting the patient to a monitoring system having more robust capabilities.

The need for continuity of data collection and display is most pressing in emergency situations. Hospital personnel want to monitor additional parameters, change the selection of parameters viewed, or retrieve additional data from the patient's history. At the same time, the patient may have to move to a different care unit. During an emergency, the speed at which a patient is transferred from a bed to an operating room or intensive care unit may substantially impact the patient's chance of survival. Hospital personnel need to be able to quickly add functionality and go.

Two major considerations in the design of monitoring systems have been ease and speed of system reconfiguration. It is particularly undesirable to connect sensors to a patient or disconnect them immediately prior to transportation or administration of critical procedures. U.S. Pat. Nos. 4,715,385 and 4,895,385 to Cudahy et al. discuss a monitoring system which includes a fixed location display unit and a portable display unit. A digital acquisition and processing module (DAPM) receives data from sensors attached to the patient and provides the data to either or both of the fixed and portable display units. Normally, the DAPM is inserted into a bedside display unit located near the patient's bed. When it is necessary to reconfigure the system for transporting the patient, the DAPM is connected to the portable display and then disconnected from the bedside display. The DAPM remains attached to the patient during this reconfiguration step and during patient transport, eliminating the need to reconnect the patient to intrusive devices. Once the DAPM is disconnected from the bedside display, a transportable monitoring system is formed, comprising the portable display and DAPM.

Besides the time delays which may be encountered when adding sensors to the monitor configuration, systems in the prior art also leave much to be desired with respect to cable management. A large number of cables extend between the patient and the monitor. In the past, there has been at least one cable added for each parameter monitored. For example, there may be five cables for EKG, two for cardiac output, two for temperature, plus four hoses for measuring blood pressure using invasive sensors. This array of cables and hoses interferes with the movement of personnel around the patient's bed. The greater the number of cables and hoses, the greater the risk that someone will accidentally disrupt one of them. This has been a common problem in previous systems from several vendors.

Furthermore, the digital acquisition and processing module of the Cudahy et al. system has a fixed parameter configuration, and if the parameter requirements change due to a change in condition of the patient, the digital acquisition and processing module must be disconnected and a different module including the new parameters which are required to be monitored must be connected. This process is not only time consuming, due to the reconnection of the sensors and cables between the patient and the module, but also destructive of data since patient data acquired in the first processing module is lost when it is disconnected and is not transferred to the subsequent processing module. Furthermore, the processing module of Cudahy et al. is extremely bulky and difficult to position near a patient. In order to use the fixed display to observe data from the DAPM, the DAPM must be inserted into the fixed display. And furthermore, the processing module of Cudahy et al. requires extensive cabling to the different patient sensors, which further adds to the complexity and setup time of the system.

Additional simplification of the steps performed to reconfigure the system is also desirable in order to reduce the time to prepare the patient and monitoring system for transportation to an operating room or intensive care unit.

SUMMARY OF THE INVENTION

The present invention is embodied in patient monitoring apparatus for display on a display device of patient data. The apparatus is adapted for use in a system which includes a plurality of sensors. The patient data are collected from a medical patient using the plurality of sensors.

The apparatus includes a data acquisition cartridge which selectively communicates with the plurality of sensors. The data acquisition cartridge collects patient data from a selected sensor and transmits conditioned data signals produced from the patient data to a portable monitor.

The apparatus also includes an independently positionable, self contained data acquisition pod. The data acquisition pod selectively communicates with the plurality of sensors. The data acquisition pod is adapted to collect further patient data from a further selected sensor. The data acquisition pod transmits the further conditioned data signals produced from the patient data to the portable monitor.

The portable monitor detachably couples to the data acquisition cartridge and the data acquisition pod. The portable monitor receives and stores the conditioned data and the further conditioned data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1ais a block diagram of an exemplary patient monitoring system in accordance with the invention.

FIG. 1bis an isometric view of the patient monitoring system shown in FIG. 1a.

FIG. 2 is a block diagram of a printed circuit board within the patient monitoring system shown in FIG. 1a.

FIG. 3 is a block diagram of a printed circuit board within the patient monitoring system shown in FIG. 1a.

FIG. 4 is a block diagram of a data acquisition pod shown in FIG. 1a.

FIG. 5 is an isometric view of a cartridge shown in FIG. 1a.

FIG. 6 is an isometric view of the docking station shown in FIG. 1a.

FIG. 7 is a flow diagram of the memory update process used in the system shown in FIG. 1a.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTOverview

An exemplaryportable monitor assembly100 in accordance with the present invention is shown in FIG. 1a. Aportable monitor102 is detachably coupled to and acquires physiological data signals from a plurality of data acquisition modules. The data acquisition modules includedata acquisition pods150,152,154,155,156 and158 anddata acquisition cartridges160 and162. The pod basically combines the patient data into a single output signal, whereas the cartridges combine patient data and may also include signal processing and sensor support devices. The pods150-158 are advantageously small, and may be placed in a variety of locations, providing a high degree of flexibility to medical personnel. The pods150-158 provide cable management capability because each pod is connected to monitor102 by, at most, one cable, regardless of how many sensors are coupled to the pod. The pods150-158 andcartridges160 and162 may be attached to both invasive and non-invasive sensors (not shown) for collecting physiological data from a patient. As used herein, the detachable coupling of the data acquisition modules, and in particular for pods150-156, is intended to include any manner of communicating the acquired data signals to monitor102, such as a wireless communication link.

Many prior art systems required insertion of the cartridges (modules) into a bulky box or into a display. The data acquisition pods in the present invention are standalone (self-contained) devices. In addition, they connect directly to thecase103 of theportable monitor102. There is no need to insert the pods into a bulky box, or into a display unit, to display data. As a result the monitor-pod configuration need not be changed to transport the patient. No additional connections need be established between the monitor and the pods, and no connections need be detached.

Pods150-158 andcartridges160 and162 may be connected toportable monitor102 independently of one another. To add function to the monitoring system for a higher level of care, an additional pod150-158 orcartridge160 or162 may be added without affecting any other modules that are already coupled to monitor102. There is no need to reconfigure the entire system to add a module.

Pods150-158 are independently positionable, both from one another, and frommonitor102. In accordance with the present invention, pods150-158 may be placed in any convenient location close to the patient. Each pod may be placed at a different location if desired, to minimize the lengths of the cables and hoses connecting the patient to the respective pods. Alternatively, the pods may be collocated, so that all of the cables and hoses are confined to a single region. Either method enhances cable management.

Theportable monitor102 displays the physiological data and includes means for detachably mounting data acquisition cartridges, which may include a Non-Invasive Blood Pressure (NIBP)cartridge160 and/or an end-tidal cartridge162 (for measuring airway carbon dioxide). A threechannel recorder164, and abattery pack166 may also be detachably connected toportable monitor102. Each device160-166 is configured to provide both electrical and mechanical couplings when the device is mounted on themonitor102. Eachcartridge160 and162 andrecorder166 provide their own return circuits with 5000 volts isolation from the portable monitor ground, to prevent current flow from the patient to earth ground by way of the cartridge and monitor102. Theportable monitor102 has a user-accessible slot for one random access memory card (or RAM card)106 which allows easy removal and storage of patient data, such as demographic and physiological trend data. The memory card may also be used to transfer replacement software instructions to the portable monitor.

Each pod150-158 receives analog data signals from a plurality of sensors, and combines the data from the plurality of sensors into a combined analog data signal. The combined analog data signal is then converted to a digital output channel which is coupled toportable monitor102. By channeling patient data signals from many sensors into a single cable for transfer to monitor102, the desired cable management is achieved. For example, ifpod150 is located at or on the bed, the number of cables between the bed and monitor102 is reduced from eight to one.

Abase EKG pod150 provides connections for a five electrode (7 lead) EKG, one connection for a pulse oximetry (SpO₂) sensor, and two multifunction receptacles for measuring temperature, impedance respiration and/or cardiac output.

In the exemplary embodiment, two special purpose pods are available as alternatives topod150. Adiagnostic pod156 accepts data from the same sensors asbase pod150, and also has five extra leads which may be used for EEG or for a 12 lead EKG. Aneonatal pod158 has input terminals for the same types of data asdiagnostic pod156, plus an additional terminal for a transcutaneous oxygen or carbon dioxide sensor.Pod152 includes channels for mounting four pressure transducers and two additional temperature sensors. Alternatively,Pod154 may be used to collect data from two pressure transducers.Catheter Pod155 provides oximetry data (SvO₂). Further pods performing different functions may optionally be added and would be understood by those skilled in the art.

In accordance with one aspect of the invention,portable monitor102 is detachably coupled to adocking station110 which may be positioned near the patient's bed (e.g., on the bed, a bed rail, a wall, an intravenous pole or a shelf). In accordance with another aspect of the invention,portable monitor102 anddocking station110 provide complementary services. Monitoring devices which attach to the patient's body or are transported with the patient are coupled to theportable monitor102; whereas devices and services which are fixed in the room or are to be made continuously available in the room are coupled to the docking station.

Thedocking station110 providesportable monitor102 with a full suite of power and communications services. These services allowportable monitor102 to perform functions previously performed primarily through the use of large, fixed monitoring systems. At the same time, the simple connection between thedocking station110 and monitor102 allows rapid disconnection ofmonitor102 for transporting the patient. The user merely picks upmonitor102 fromdocking station110 to prepare monitor102 for transport.Docking station110 recharges the battery ofmonitor102 while the monitor is in the docking station, so that in most instances, it is not even necessary to install a battery pack to transport the patient.

Docking station110 provides mechanical support for mounting theportable monitor102, as well as electrical couplings to a remote display device120 (typically a bedside display),power114,large display122, andtelevision display124.Remote display device120 may be a fully functioning monitor including processing and display functions, or just a slave display receiving signals from the docking station for display.Docking Station110 can also communicate with several local area networks (LANs).Docking station110 provides a simple mechanism to connectportable monitor102 with several devices and networks without the need to connect individual cables. Data and power connectors ondocking station110 and on thecase103 ofportable monitor102 allow physical and electrical connections to be established concurrently. Althoughdocking station110 may be coupled to networks and remote stations outside of the patient's room, docking station need not mount on the wall to connect to these networks and stations.Docking station110 may be connected to awallbox140 to provide the additional communications links.

Although theportable monitor102 as described in the exemplary embodiment performs the functions of a multi-function bedside monitor when attached todocking station110, it may be desirable to use theportable monitor102 in conjunction with an additionalremote display120. For example, in the operating room, theremote display120 may be a slave display so as to provide a larger or more easily readable display. Theremote display120 may be a conventional, fully functioning bedside patient monitoring unit which receives, stores, displays and transmits medical data. Alternately, theremote display120 may be an intelligent workstation with a VGA display and conventional disk storage. Theportable monitor102 also includes aport127 for optionally connecting the portable monitor directly to aremote display120 when the portable monitor is not indocking station110.

Upon establishment of a connection betweenportable monitor102 anddocking station110,assembly102 determines whether the most recent physiological data for the patient is stored in the assembly or in aremote display120 coupled todocking station110. The more recent data are then copied to the device (display monitor102 or remote display120) having the less recent data (assuming that theremote display120 has processing capability). A conventional memory card106 (shown in FIG.2), is used to transfer data between theportable monitor102 and theremote display120. It is understood by those skilled in the art that, as an alternative to using a memory card for data transfers, the data may be directly transferred by a communications link.

Once theportable monitor102 is coupled to theremote display120, and the data in the two monitors are synchronized by thememory card106 transfer discussed above, all patient data received by theportable monitor102 are transferred to theremote display120. In this manner, patient data are stored redundantly inremote display120 andportable monitor102. The patient can be switched from oneportable monitor102 to another102′ (not shown) by transferring the memory card to the secondportable monitor102′, and from oneremote display120 to another120′ (not shown) without any loss of data, or any break in the continuity of the data.

According to another aspect of the invention, display setup data are stored inportable monitor102. The setup data are used to define which waveforms and which parameters appear in the available screen areas. Unlike the systems in the prior art, the setup data inmonitor102 are independent of which sensors are furnishing data, or which display is used (Whereas in the prior art, the setup data were typically stored in the display and were entered by the user each time a new display was attached to the monitor). The setup data are applied when the display is coupled to monitor102 and turned on. If the display is configured to display the waveform being monitored,portable monitor102 places the data in the appropriate areas of the display. If the display is not configured to display the waveform, then it is not displayed until the user selects the waveform on the display.

FIG. 1bshows the physical configuration of themonitor assembly100 of FIG. 1a. Porizable monitor102 is mounted ondocking station110, providing physical support, power, and communications.Monitor102 acquires physiological data signals fromdata acquisition pods150 for EKG data and152 for pressure data. The non-invasiveblood pressure cartridge160, the end tidal CO₂cartridge162, a hardcopy output device such asrecorder164 and the battery back166 are individually attached toportable monitor102 for purposes of illustration.

DETAILED DESCRIPTIONPortable Monitor

As shown in FIGS. 1aand1b,portable monitor102 is the core of a modularpatient monitoring system100.Portable monitor102 includes an integrated liquid crystal display (LCD)104. Peripheral devices may be coupled to theportable monitor102, including input devices (e.g.,pods150,152,154,155,156,158 andcartridges160 and162) and output devices (e.g.,recorder164 and cathode ray tube (CRT)display120 and LCD122). A possible minimum configuration of the exemplary embodiment includesportable monitor102, an EKG pod (150,156 or158) and thebattery pack166. Additional pods (152,154 and/or155) and cartridges (160,162) may be substituted or added, depending on the types of trend data desired for each specific patient.Portable monitor102 may be directly connected to additionalexternal displays120 and122 throughanalog output ports172. Alternatively,portable monitor102 may be detachably mounted on a docking station, such asdocking station110, which can provide couplings to both power and communications networks.Portable monitor102 receives power fromdocking station110 through aconnector125.

FIG. 2 is a block diagram showing the interaction of the components ofportable monitor102.Portable monitor102 includes two printed circuit boards (PCBs): aprocessor PCB200 and aperipheral PCB220.Processor PCB200 provides processing and storage resources for algorithm computation and for controlling system operations. In conjunction with peripheral printed circuit board (PCB)220,Processor PCOB200 controls the acquisition of data from the pods and cartridges, the processing of patient data, display of parameters and waveforms, alarms and Ethernet™ and multi-vendor connectivity.

Processor202 may be a Motorola 68EC040 or comparable processor. It controls the operation ofportable monitor102 and performs the non-numerically intensive arithmetic computations. Some numerically intensive computations are performed by components onperipheral PCB220, and are discussed below. A 32 bit processor bus, which may be Multibus II, provides theprocessor202 access to the other devices on theprocessor PCB200.

Three memory systems are located on theprocessor PCB200. A boot erasable programmable read only memory (EPROM)230 provides the initial program startup, system console support, and the method to erase and download software into the flash EPROM (FPROM)232. The EPROM may include 27C1024, 27C2048 or 27C4096 devices, which allow two wait state operation for theprocessor202. The EPROM has a total memory size of 256 KB to 1 MB, with 32 bit access.

Flash EPROM232 contains the executable code.Flash EPROM232 is programmed onprocessor PCB200 under the control ofprocessor202.Flash EPROM232 may include AMD/NEC 28F020 or 28F040 devices, which allow two wait state operation. Flash EPROM has a total memory size of 2 to 4 MB of memory, with 32 bit access.Flash EPROM232 supports a line burst fill mode of operation.

A dynamic random access memory (DRAM)208 provides program data space. The system may also be set to a development mode, in which executable code is placed inDRAM208.DRAM208 may include NEC D424190 or HM514280 devices, which allow 2 wait state operation. TheDRAM208 has a total memory size of 1 MB of memory. The memory is organized as 32 data bits and 4 parity bits.

Processor PCB200 includessupport circuitry203 forprocessor202.Circuitry203 includes: DRAM parity generation and checking236; twointerval timers240 and242; awatchdog timer238, an interrupthandler244, a serialdiagnostic port234,memory mode selection248, bus error time-out246 and PC memory commoninterface adaptor control247. In the exemplary embodiment,support circuitry203 is implemented in application specific integrated circuits (ASIC).

Parity circuit236 generates odd parity on memory writes and checks for errors on memory reads. If an error is detected, a parity error flag is set on a byte basis.

Twointerval timers240 and242 are provided for time measurement. Thefirst timer240 has a range of 0.1 to 12.7 milliseconds (msec). Thesecond timer242 has a range of 1 to 127 msec. The user selects the interval for each timer. If either timer is enabled and counts to the specified interval, an interrupt flag is set.

Watchdog timer238 allows selection of a timeout interval between 0.01 and 1.27 seconds. The user selects the interval. During system startup,watchdog timer238 is disabled. Iftimer238 is enabled and counts to the specified value during execution of any process, an interrupt flag is set. If the interrupt is not serviced within predetermined interval, a processor reset is generated.

Interrupthandler244 prioritizes the various interrupt sources into seven levels for the processor. The interrupts may be generated bywatchdog timer238,parity checker236,timer240,peripheral PCB220,timer242,graphics controller254, ordiagnostic port234.

Diagnosticserial port234 provides a receive and transmit communications channel at 1.2, 9.6, or 19.2 Kbits per second, with 8 data bits, no parity, and 1 stop bit. The choice of the data rate is determined by a programmable parameter value. Data transfers are supported by polled status and interrupt control. Internal loopback may be programmed.

Memory mode selection248 controls the allocation of normal program execution space to the three physical memory devices: bootEPROM230,flash PROM232 andDRAM208. During system startup, the execution space is allocated onboot EPROM230.

The bus error time-out function246 activates a 10 microsecond timer when a bus cycle starts. The bus error is activated if a data acknowledge signal is not received within the 10 microsecond time period.

Bus master circuit206 onprocessor PCB200 maps a 16 Mbyte peripheral space into the address space ofCPU202. In the exemplary embodiment,CPU202 has a 32bit data bus212 and peripheral bus328 (as shown in FIG. 3) includes a 16 bit data bus. In order to accommodate the different bus data paths,bus master206 includes a circuit to split each 32 bit word received fromCPU202 into two 16 bit words whichperipheral bus328 can accept. Each pair of 16 bit words is transmitted over two peripheral bus cycles.

A conventional randomaccess memory card106 is used for information storage and transfer. The memory card interface is controlled by the PC memory common interfaceadaptor control function247 ofASIC203.Memory card106 is a credit card sized encapsulated circuit board containing static RAM and a small battery. The information stored in thememory card106 includes setup data (e.g., alarm limits), patient specific demographic and physiological trend data, and software.

Typically,memory card106 will be used when transferring patient data between two differentportable monitors102. Such transfers typically occur when a patient moves from one care unit (e.g., intensive care unit, operating room, or recovery room) to another. When used for storing software,memory card106 provides a convenient mechanism for downloading software upgrades toportable monitor102, which are then stored in aflash EPROM232, shown in FIG.3. When used for these purposes,memory card106 may be removed fromportable monitor102, except when in use for data or software transfers.

Another possible use ofmemory card106 may be to associate a respective card with each patient from admission to checkout, providing rapid access to the patient's history at any time during his or her stay in the hospital. When used for this purpose,memory card106 may remain inportable monitor102 at all times between patient admission and discharge, except when the card is transferred between two portable monitors. All patient trend data would be stored, in a particular memory card and continuously upgraded at appropriate intervals.

Still another use for the memory card is for software maintenance and upgrades. A new (second) set of instructions may be downloaded to theFlash EPROM232 from thememory card106 to replace the existing (first) set of instructions.

FIG. 3 is a block diagram ofperipheral PCB220 shown in FIG.2.Peripheral PCB220 manages the interfaces betweenportable monitor102 and all external devices and networks to which it may be connected.Peripheral PCB220 is coupled to aport327 ofprocessor PCB200. Aperipheral bus328, which may use conventional Intel Multibus format, couplesprocessor202 and the devices on theperipheral PCB220.Peripheral bus328 includes a 16-bit data path and a 24-bit address space, and has a bandwidth of at least 8 Mbytes/second.

Multiple bus masters can accessperipheral bus328, under the control of anarbiter361, described below. The bus masters include:host bus master206 forprocessor202; two digital signal processors (DSPs)330aand330bfor preprocessing the data acquisition samples; a carrier sense multiple access/collision detection (CSMA/CD) controller direct memory access (DMA)channel362; two DMA channels344aand344bfor transmitting commands to pods150-158 andcartridges160,162 and for receiving sample data from the pods and cartridges; and a DMA channel for transmitting data tothermal recorder164. When one of these bus masters (which may be either206,334,362,344a,344bor358) usesbus328,processor202 gives permission and releases control of address, data and strobe lines (not shown) in thebus328. Thebus master206,334,344a,344b,358 or362 then places memory addresses onbus328, directing DMA data transfers to send or receive data.

The DSP DMA control is implemented in a bus master application specific integrated circuit (ASIC)334.Bus master circuit334 connected to the DSPs330aand330ballows the DSPs to access theentire memory space322 viaperipheral bus328. DSPs330aand330baccess bus328 by an indirect method. The DSP first writes to an address register334ainbus master334. This address points to the desired address onperipheral bus328. After loading the address, the DSP may write to locations onbus328. After each word is written, the lower sixteen address lines (not shown) will automatically increment, allowing efficient moves of block data.

Bus Master334 may also operate in slave mode, allowing theCPU202 to arbitrate DSPs'330aand330bcommunications withperipheral bus328. In this mode,CPU202 can write directly into the DSPs' static random access memories (SRAM)332aand332b. This capability is used during initial download of the DSP code from CPU flash programmable read only memory (FPROM)232 as shown in FIG.2.CPU202 may also use this capability to deposit variables to and retrieve variables from DSPs330aand330b. All other bus masters (DMA channels344a,344b,358 and362) are prevented from accessing the DSPs' SPEM332aand332bin this manner, to ensure the integrity of the DSP code.

DMA channels344a,344b,358 and362 useperipheral bus328 to read and write sharedSRAM memory322 andperipherals150,152,154,155,156,158,160,162, and164. Channels344aand344bare used for data acquisition frompods150,152,154,155,156,158 and/orcartridges160,162. Channels344a,344bsend commands and timing information to the pods and cartridges, and receive data and status from them.

When receiving data, channels344a,344bwrite the received data to respective buffers every two milliseconds (msec). After five consecutive two msec cycles, the data in the buffers are written over with new data. To ensure transfer of the data to the sharedmemory322 for storage, two different types of interrupts are generated within channels344aand344b. The first interrupt is generated every two msec when data are placed in the buffer. The second interrupt is generated each time five blocks of data are received, i.e., every ten msec.

DMA channel358 is a special purpose thermal head driver forrecorder164. This channel combines data from three different locations in sharedmemory322 to overlay grid, text and waveform data.Channel358 also chains together print pages of varying length for outputting the data torecorder164. The output signal fromchannel358 is sent over aserial link386 torecorder164.

DMA channel362 is a conventional single chip CSMA/CD controller for twisted pair cable. This channel is used for communications to LANs whenportable monitor102 is placed in adocking station110.Channel362 is not operated whenportable monitor102 is removed fromdocking station110.

Data are received from the pods and cartridges by way of two cross point switches346aand346b. All pod connections are through switch346b, which provides a 5000 volt isolation between the sensor return circuits andportable monitor102 ground to guard against ground loops, which could endanger patient safety and introduce noise into the measured data. In the exemplary embodiment, crosspoint switch346adoes not provide this isolation, socartridges160,162 provide their own 5000 volt isolation between cartridge return circuits and theportable monitor102 ground. Otherwise the two crosspoint switches346aand346bare functionally and logically identical.

The crosspoint switches346a,346breceive patient data signals from the pods and cartridges and multiplex the data signals before passing them on to channels344aand344b. Each switch346aand346bcan communicate with either channel344aor344bvia separate 1.6 Mhz links348a,348b,350a, and350b.

The two DMA channels344aand344bare synchronous and are run in a master/slave configuration. Every 15.6 microseconds, there are transfers between the pods/cartridges and sharedmemory322. These transfers include two reads (one per channel344aand344b) and two writes (one per channel344aand344b) to a sharedmemory322. Sharedmemory322 includes an extra two byte word for channels344aand344bthat is fetched during each 15 microsecond transfer to configure the crosspoint switches346aand346b. The low byte is used to control the crosspoint switch of slave DMA channel344band the high byte is used to control master DMA channel344a. For eachrespective pod port364,366,368,370 andcartridge port372,374, one respective bit in the control word is used to enable power to the pod, and another respective bit is used to enable transmission of a sync signal to the pod. Thus a total of five words are transferred during each 15 msec cycle. The data samples are interleaved between the two DMA channels344aand344b.

To allow modifications to the configuration of pods and cartridges,CPU202 issues a request for identification to the pods and cartridges by way of theirrespective ports364,366,368,370,372 and374. The pod or cartridge responds with a unique identification signal.

When commanding the pods and cartridges, the channels344aand344bfetch 24 bit words from sharedmemory322. Each 24 bit word includes an 8-bit DMA control word and a 16-bit front end command. The 8-bit DMA control word includes a 3-bit slot address identifying theport364,366,368,370,372 and374 to which the command is routed and a 2-bit DSP redirection control to identify the routing of the data returned by the pod or cartridge. The 16-bit command is transferred to the pods/cartridges.

The DMA channels344aand344balso communicate with DSPs330aand330bby way of aserial interface338. All of the data received by channels344aand344bis routed to the DSPs in addition to sharedmemory322. The DSP is sent a frame sync signal from master DMA channel344aevery 2 msec.

Abus arbiter352 controls access tobus master334 and DMA channels344aand344b.Bus master circuit334 provides both round robin and prioritized arbitration. Since DMA channels344aand344bcould lose data if denied access tobus328 for an extended period, a round robin element is included in the arbitration scheme. Within the timing constraints that prevent loss of data,bus arbiter352 also allows burst mode operation, allowing multiple words to be written without entering additional wait states.Bus arbiter352 also allows burst mode operation during read cycles.

In addition to the bus masters, there are also slave devices coupled tobus328 by universal asynchronous receiver/transmitters (UARTs)354. These include twomulti-vendor ports380 and382 (MVP1, MVP2 respectively), and abattery port378.

The two DSPs330aand330bmay be conventional processors such asAnalog Devices ADSP2101 or2105 DSP chips. These are 16-bit processors with an instruction set which includes normalization and exponent derivation by barrel shifting. Since many of the operations performed in the EKG algorithms are common signal processing functions, most of the computationally intensive and simply defined processing stages may be performed in the DSPs. These stages may include finite impulse response (FIR) and infinite impulse response (IIR) filtering, cross-correlation, power spectrum estimation and others. Matrix algorithms and other numerical processing may also be performed in the DSPs.

In addition to performing signal processing tasks, DSPs330aand330bdistribute data to all of the output devices coupled toportable monitor102, including local display devices and network devices. The DSPs perform appropriate sample rate conversion, data scaling, and offsetting to the raw sample data collected bymonitor102.

Monitor102 includes a small internal battery (not shown). If external battery166 (shown in FIG. 1b) is at a low charge level, the internal battery provides power for a time period (e.g., 1 minute) which is sufficient to removebattery166 and install another external battery.

Data Acquisition Pods

FIG. 4 shows a block diagram of an exemplarydata acquisition pod150.Pod150 is self-contained. That is,Pod150 includes all of the electronics required to acquire a signal from a sensor, condition the signal and transmit the signal toportable monitor102, without insertingpod150 in themonitor102, or in a box (Pod150 is unlike prior art data acquisition cartridges which must be mechanically inserted into a separate box to couple with the monitoring system). The use of a self-contained,standalone pod150 simplifies preparing the patient for transportation. There is no need to removepod150 from a box, or to reconnect any cables between thepod150 and monitor102.

Pod150 receives patient data from a plurality of sensors410a-410nvia terminals411a-411n(orterminals16 and17 as shown in FIG.1). These sensors may measure EKG, blood pressure, pulse, temperature, EEG or other physiological parameters. Each input data stream is amplified and filtered by circuits418a-418nto remove noise and any undesirable signals which the sensors may acquire. The amplified and filtered output signals420a-420dare combined to form asingle signal415 by a combiner which may be atime division multiplexer414. The combinedsignal415 is then converted from analog form to digital form by A/D converter412.Pod150 includes a single coupling150atoportable monitor102. Signals are transmitted to coupling150aby way of a communications ASIC,416.Pod150 may also optionally include amemory432 for storing calibration data and alarm limits.Pods152,154,155,156 and158 are similar insofar as the functions shown in FIG. 4 are concerned.

The main function of the pods150-158 is data acquisition. The filtering and amplification are performed to ensure that the data furnished to monitor102 accurately represent the parameters sensed by sensors410a-410n. The application of mathematical algorithms to these data to process the signals is performed insideportable monitor102. This division of services between pods150-158 and monitor102 reduces the size of the pods150-158 relative to typical prior art data acquisition cartridges. Pods150-158 are small enough to be positioned conveniently in a variety of positions, including: on a shelf, on a bed, on a bed rail or headboard, under a pillow, or on an intravenous pole.

An exemplary patient monitoring system in accordance with the invention (shown in FIG. 1a) may include any one of a basic, diagnostic or neonatal pod. Abase EKG pod150 acquires real-time EKG and respiration waveforms as input data, which are processed by QRS, arrhythmia and S-T segment analysis algorithms in DSP's330aand330b. The sensors (not shown) inpod150 are five electrodes with leads I, II, III, IV (AVR, AVL and AVF leads) and V (chest). From this data,portable monitor102 can determine impedance respiration as well as heart rate.

Base pod150 also accepts input data from two temperature sensors which may be used for measuring nasal respiration and cardiac output (C.O.). A nasal respiration thermistor (not shown) may be used to detect respiration by sensing the changes in nasal passage temperature due to the difference in temperature between inhaled and exhaled air. C.O. data are acquired by using the thermodilution method. An Edwards type catheter (not shown) can be used to inject either cooled or room temperature water into the coronary artery. Downstream blood temperature and injectate temperatures are then measured.

Lastly,pod150 receives data representative of pulse and oximetry. Oximetry data representing the saturation, or fraction of oxyhemoglobin to functional hemoglobin (SPO₂in %O₂) are collected using absorption spectrophotometry.

As shown in FIG. 1b,pod150 includes two proximately located switches13 and15. Switch13 is coupled to a circuit which transmits a signal to monitor102 causingmonitor102 to condition itself to start the cardiac output procedure (e.g., perform range and alarm limit adjustments). The operator actuates switch13 at the same time that he or she injects the injectate into the patient for cardiac output measurement. The DSPs330aand330binmonitor102 calculate the waveform of the temperature gradient between thermistors for the cardiac output procedure. Similarly, switch15 is coupled to a circuit which transmits a signal to monitor102 causingmonitor102 to configure itself to start the wedge procedure and/or switch the display to wedge mode. (The wedge procedure is executed during a measurement of the pulmonary artery wedge pressure). The operator actuates switch15 at the same time that he or she inflates a balloon inside the patient's pulmonary artery for pulmonary artery wedge pressure measurement. Switches13 and15 are conveniently co-located on pod150 (near the sensors on the patient). This facilitates concurrent actuation of switch13 while starting the cardiac output measurement, and facilitates concurrent actuation of switch15 while starting the wedge procedure.

Systems in the prior art typically featured the cardiac output switch13 and wedge switch15 on themonitor102. It is more convenient to locate switches13 and15 close to the patient (as in the present invention) than on monitor102 (as done in the prior art), because the operator is close to the patient while injecting liquid (for measuring cardiac output) or inflating a balloon in the patient's artery (for a pulmonary artery wedge pressure measurement). Becausepod150 is small and is easily located close to the patient,pod150 is an advantageous device on which to locate switches13 and15. In some hospital room configurations, it may be desirable to place monitor102 too far away to conveniently accessmonitor102 while starting the procedures, making the switch location onpod150 advantageous. Furthermore, safety is enhanced, because the operator does not have to walk around the lines (e.g., lines18 and34) connected to monitor102.

Diagnostic pod156 includes input terminals to receive data from sensors similar to those used in conjunction withbase pod150. In addition, the diagnostic pod accepts five further leads for receiving EKG data from additional electrodes which may be placed on the patient's chest. Alternatively, additional terminals may be used to receive EEG data.

Neonatal pod158 includes input terminals similar todiagnostic pod156. In addition,neonatal pod158 includes terminals for receiving long-term, non-invasive, transcutaneous data for monitoring the partial pressures of oxygen and carbon dioxide. In addition to transcutaneous monitoring, a general gas bench for blood gas analysis may be included.

In addition to one of theabove EKG pods150,156 or158, an exemplary patient monitoring system in accordance with the invention may include a pressure pod152 (or154) and/or anoximetry catheter pod155.Pressure pod152 accepts data from 4 invasive pressure sensors, which are fluidly coupled to strain gage transducers, and accepts data from 2 temperature sensors.

Referring again to FIG. 1b, thepressure pod152 has a zeroswitch42 conveniently located onpod152, where it is easily actuated while calibrating sensors (not shown) by exposing them to atmospheric pressure. Actuating the zero switch causespod152 to transmit a zero signal to monitor102, causingmonitor102 to reset the value of its waveform to zero in response to the voltage currently detected across the sensor. Asecond switch44 located onpod152 sends a further signal to monitor102, causingmonitor102 to condition itself to begin a wedge procedure. The response ofmonitor102 to this further signal is the same as described above with respect to actuation of switch15 onpod150. As described above with respect topod150, the location of the control switches on the pod (near the patient) simplifies operations.

Pressure/Temperature pod154 accepts data from two transducers. Thecatheter pod155 receives data from a catheter inserted into the patients artery.

It is understood by one skilled in the art that many different embodiments of the data acquisition pod may be developed to meet different data acquisition requirements. Both the types of sensors used and the number of sensors of each type may be varied.

Data Acquisition Cartridges

FIG. 5 shows the mechanical configuration of an exemplary non-invasiveblood pressure cartridge160. In contrast to pods150-158,cartridge160 is not independently positionable, but mounts onmonitor102.

Cartridge160 accepts data vialine19 for oscillometric measurement of systolic, diastolic, and mean arterial pressures from a cuff transducer (not shown).Cartridge160 performs functions similar to the pod functions shown in FIG.4. In addition, the cartridge provides a separate 5000 volt isolation between the cartridge return circuit and the portable monitor ground for safety and to reduce undesirable noise.

As shown in FIG. 5,cartridge160 includes a suitable mechanism to attach itself toportable monitor102. This may be in the form of a guide piece160awith a latch160c. Guide piece160aslides into a mating guide (not shown) onportable monitor102, engaging connector160bwith a mating connector129 (shown in FIG. 1a) on the monitor, and engaging the latch160cwith a mating catch (not shown) on the monitor in a single operation. Many variations in the shape of guide piece160aand latch160cmay be used to provide the mechanical coupling at the same time that connector160bis engaged to provide electrical coupling. Mountingcartridge160 directly to monitor102 is convenient and uses space efficiently; a bulky box is not needed to house the cartridge.

The end-tidal CO₂Cartridge162,recorder164 andbattery pack166 each use a similar coupling technique, to facilitate reconfiguration of theportable monitor102. The end-tidal CO₂Cartridge162 receives data representing inhaled and exhaled carbon dioxide partial pressures from an airway adapter (not shown) vialine21, and engages connector131 (shown in FIG.1). Therecorder164 is a conventional three channel thermal printer. Thebattery pack166 includes a conventional nickel-cadmium battery.

As with the data acquisition pods, the data acquisition cartridge may be practiced in a number of alternative embodiments. Both the types of sensors used and the number of sensors of each type may be varied. Preferably, data acquisition modules which are bulky, heavy, or consume large amounts of power are implemented as cartridges, while small, lightweight low power data acquisition modules are implemented as pods. For example,pressure cartridge160 includes a motor and pneumatic devices, in addition to the filters, amplifiers, multiplexer and A/D converter. In considering whether a new type of sensor should be added to a pod or a cartridge, isolation requirements may be a factor, since each cartridge provides its own isolation.

Docking Station

FIG. 6 showsdocking station110 to whichportable monitor102 may be attached. A connector110aprovides data communications couplings to the portable monitor. A guide110b, which may be integral with connector110aas shown in FIG. 6, facilitates proper positioning ofmonitor102 ondocking station110, and assists in maintainingmonitor102 in position whilemonitor102 is ondocking station110. A separate connector110gprovides power. Respective connectors110cand110dprovide power and data communications links fromportable monitor102 to external power sources, devices and networks, whenmonitor102 is ondocking station110. Connector102dmay be a conventional connector to interface directly to an Ethernet™ LAN118 (shown in FIG.1A). Additionally, the data may be output to aremote display120 or122, or to an intelligent workstation, for display in VGA format.

An optional clamp110emay be used to mount a docking station on an intravenous pole (not shown). Alternatively, clamp110emay be omitted and backplate110fmay be fastened directly to a wall or bed.

Many variations of the docking station mechanical configuration are possible. For example, connector110aand guide110bmay be separate from one another. There may be multiple connectors110aand/or multiple connectors110d. Additional mechanical fasteners may be added to improve the stability of the detachable mounting.

Connector110dmay alternatively connect to asmart wallbox140, as indicated in FIG. 1a. The wallbox converts the twisted pair CSMA/CD signal from line136 (shown in FIG. 1a) to 10 Mbits/second Thinnet, which uses the IEEE 802.3 Type 10-Base-2 standard. This connection provides a LAN connection betweenportable monitor102 and remote stations which may be patient monitoring systems or computers. Aseparate connection138 provides 1 Mbit/second communications with an input/output device LAN, which may include keyboards, pointing devices, voice input, bar code readers and label printers. Eight additional multi-vendor ports (MVP)130 are provided. Four analog output ports provide waveform data for transmission to external devices (e.g., monitors, recorders).Wall box140 assigns ID numbers to devices which connect to it. This allows the portable monitor to automatically identify any changes to the configuration devices connected to thewall box140.

Data Transfers During Connection

FIG. 7 is a flow diagram showing steps which are performed automatically to update the patient data inportable monitor102 memory (the portable monitor data storing means), or the data inremote display120 memory (assuming thatremote display120 has storage), so that both are kept current. Atstep750,portable monitor102 is inserted indocking station110, and the connection to theremote display120 is established. Atstep752, memory in theremote display120 is checked for data. If there are no data then patient physiological data stored in theportable monitor102 is downloaded toremote display120 memory atstep754. If there are data inremote display120, atstep756, a determination is made whether the data inremote display120 and the data inportable monitor102 are associated with the same patient. A double comparison is made; both patient name and patient identification are compared. If either the name or the ID do not match, or if either the name or ID is blank, then the data in theportable monitor102 andremote display120 are considered to be associated with two different patients.

If the data are from two different patients, atstep758remote display120 will prompt the operator to choose either the data inremote display120 or the data inportable monitor102. Once the operator has selected one of the sets of data, atstep760 the data are copied fromremote display120 to theportable monitor102 ifremote display120 is selected, or fromportable monitor102 toremote display120 ifportable monitor102 is selected.

If it is determined atstep756 that the data inremote display120 andportable monitor102 are associated with the same patient, then atstep762, a determination is made whether the data inremote display120 are newer than the data inportable monitor102. If the portable monitor data are newer, then atstep764 the portable monitor data are copied toremote display120. If the remote display data are newer, then atstep766, the remote display data are copied toportable monitor102.

The same sequence of steps is performed whenmemory card106 is inserted intomonitor102, except that monitor102 exchanges data withmemory card106 instead ofremote display120. It is understood that replacingdisplay120 withmemory card106 insteps750 through766 above, the data inmonitor102 andmemory card106 are kept current.

It is understood by one skilled in the art that many variations of the embodiments described herein are contemplated. While the invention has been described in terms of exemplary embodiments, it is contemplated that it may be practiced as outlined above with modifications within the spirit and scope of the appended claims.

Claims (6)

What is claimed:

1. Patient monitoring apparatus for displaying, on a display device, medical data processed by a monitor and collected from a patient during a patient monitoring mode of operation using a plurality of sensors, the apparatus adapted for use in a system which includes a plurality of sensors, the apparatus comprising:

a portable monitor, enclosed in a first housing, for receiving and processing patient data during said patient monitoring and developing therefrom signals suitable for causing display of the patient data on a display device during said patient monitoring;

a data acquisition cartridge, enclosed in a second housing, coupled for communicating with a selected one of the plurality of sensors, the data acquisition cartridge adapted for collecting patient data from a selected sensor, for conditioning the collected patient data and for transmitting the conditioned data to said portable monitor for processing therein during said patient monitoring; and

an independently positionable, self contained data acquisition pod, enclosed in a third housing, coupled for communicating with a selected one of the plurality of sensors, the data acquisition pod adapted for collecting further patient data from a further selected sensor, for conditioning the further patient data and for transmitting the conditioned further patient data to said portable monitor for processing therein during said patient monitoring; wherein

said first housing includes first coupling means for detachably coupling to said second housing, which first coupling means co-locates the data acquisition cartridge with the portable monitor during said patient monitoring, and the first housing includes second coupling means for detachably coupling to said third housing for receiving said patient data transmitted from said data acquisition pod to said portable monitor, which second coupling means allows said data acquisition pod to be independently positionable, self-contained, and not co-located with the portable monitor during said patient monitoring, and wherein the data acquisition pod comprises:

means for receiving a plurality of patient physiological parameter data from the plurality of sensors; and

means for generating from the plurality of physiological parameter data a digital data signal which is transferred to the portable monitor.

2. Apparatus in accordance with claim1, wherein the generating means include:

means for producing a time division multiplexed signal from the patient data; and

means for converting the multiplexed signal to a digital data signal, wherein the conditioned signal is a time division multiplexed digital data signal.

3. Apparatus in accordance with claim1, in which the data acquisition pod further includes a connection for a ventilator and means for receiving data representing at least one parameter from the group consisting of blood gas saturation, 12 lead electrocardiogram and electroencephalogram.

4. Patient monitoring apparatus for displaying, on a display device, medical data processed by a monitor and collected from a patient during a patient monitoring mode of operation using a plurality of sensors, the apparatus adapted for use in a system which includes a plurality of sensors, the apparatus comprising:

a portable monitor, enclosed in a first housing, for receiving and processing patient data during said patient monitoring and developing therefrom signals suitable for causing display of the patient data on a display device during said patient monitoring;

a data acquisition cartridge, enclosed in a second housing, coupled for communicating with a selected one of the plurality of sensors, the data acquisition cartridge adapted for collecting patient data from a selected sensor, for conditioning the collected patient data and for transmitting the conditioned data to said portable monitor for processing therein during said patient monitoring; and

an independently positionable, self contained data acquisition pod, enclosed in a third housing, coupled for communicating with a selected one of the plurality of sensors, the data acquisition pod adapted for collecting further patient data from a further selected sensor, for conditioning the further patient data and for transmitting the conditioned further patient data to said portable monitor for processing therein during said patient monitoring; wherein

said first housing includes first coupling means for detachably coupling to said second housing, which first coupling means co-locates the data acquisition cartridge with the portable monitor during said patient monitoring, and the first housing includes second couplings means for detachably coupling to said third housing for receiving said patient data transmitted from said data acquisition pod to said portable monitor, which second coupling means allows said data acquisition pod to be independently positionable, self-contained, and not co-located with the portable monitor during said patient monitoring;

the data acquisition pods includes means for receiving patient electrocardiogram data, blood oxygen saturation data and either one of temperature data and cardiac output data;

the data acquisition pod transmits first and second control signals to the portable monitor, and wherein the portable monitor includes:

a display device adapted to display first and second waveforms representing cardiac output data and blood oxygen saturation levels, respectively;

means for configuring the display device for a cardiac output measurement in response to the first control signal; and

means for configuring the display device for a wedge procedure in response to the second control signal.

5. Patient monitoring apparatus for displaying, on a display device, medical data processed by a monitor and collected from a patient during a patient monitoring mode of operation using a plurality of sensors, the apparatus adapted for use in a system which includes a plurality of sensors, the apparatus comprising:

a portable monitor, enclosed in a first housing, for receiving and processing patient data during said patient monitoring and developing therefrom signals suitable for causing display of the patient data on a display device during said patient monitoring;

a data acquisition cartridge, enclosed in a second housing, coupled for communicating with a selected one of the plurality of sensors, the data acquisition cartridge adapted for collecting patient data from a selected sensor, for conditioning the collected patient data and for transmitting the conditioned data to said portable monitor for processing therein during said patient monitoring; and

an independently positionable, self contained data acquisition pod, enclosed in a third housing, coupled for communicating with a selected one of the plurality of sensors, the data acquisition pod adapted for collecting further patient data from a further selected sensor, for conditioning the further patient data and for transmitting the conditioned further patient data to said portable monitor for processing therein during said patient monitoring; wherein

said first housing includes first coupling means for detachably coupling to said second housing, which first coupling means co-locates the data acquisition cartridge with the portable monitor during said patient monitoring, and the first housing includes second coupling means for detachably coupling to said third housing for receiving said patient data transmitted from said data acquisition pod to said portable monitor, which second coupling means allows said data acquisition pod to be independently positionable, self-contained, and not co-located with the portable monitor during said patient monitoring,

wherein the data acquisition pod, includes means for receiving data representative of patient blood pressure data, and transmits first and second control signals to the portable monitor, and wherein the portable monitor includes;

a display device adapted for displaying first and second waveforms representing blood pressure and pulmonary artery wedge pressure, respectively, the first waveform being generated from a signal representing blood pressure, the signal representing blood pressure being received from the data acquisition pod;

means for causing the display device to associate the signal representing blood pressure with a display value of zero for the first waveform, in response to the first control signal; and

means for configuring the display device for a wedge procedure in response to the second control signal.

6. Patient monitoring apparatus for displaying, on a display device, medical data processed by a monitor and collected from a patient during a patient monitoring mode of operation using a plurality of sensors, the apparatus adapted for use in a system which includes a plurality of sensors, the apparatus comprising:

a portable monitor, enclosed in a first housing, for receiving and processing patient data during said patient monitoring and developing therefrom signals suitable for causing display of the patient data on a display device during said patient monitoring;

a data acquisition cartridge, enclosed in a second housing, coupled for communicating with a selected one of the plurality of sensors, the data acquisition cartridge adapted for collecting patient data from a selected sensor, for conditioning the collected patient data and for transmitting the conditioned data to said portable monitor for processing therein during said patient monitoring; and

an independently positionable, self contained data acquisition pod, enclosed in a third housing, coupled for communicating with a selected one of the plurality of sensors, the data acquisition pod adapted for collecting further patient data from a further selected sensor, for conditioning the further patient data and for transmitting the conditioned further patient data to said portable monitor for processing therein during said patient monitoring; wherein

said first housing includes first coupling means for detachably coupling to said second housing, which first coupling means co-locates the data acquisition cartridge with the portable monitor during said patient monitoring, and the first housing includes second coupling means for detachably coupling to said third housing for receiving said patient data transmitted from said data acquisition pod to said portable monitor, which second coupling means allows said data acquisition pod to be independently positionable, self-contained, and not co-located with the portable monitor during said patient monitoring, and

the portable monitor includes:

means for transferring data to a remote display device which has a remote display memory for storing the patient data;

means for receiving data from the remote display device;

a portable monitor memory for storing the patient data;

means for determining whether the data stored in the portable monitor memory are older than the data stored in the remote display memory;

replacing means for replacing the data stored in the portable monitor memory with the data stored in the remote display memory if the data stored in the portable monitor memory are older than the data stored in the remote display memory; and

means for transmitting the data stored in the portable monitor memory to the remote display memory if the data stored in the remote display memory are older than the data stored in the portable monitor memory.

Images